Sunrise & Sunset

In the Vedic panchang system, the day begins at sunrise rather than midnight. This means every time-dependent calculation — which tithi is active "today," when Rahu Kaal falls, how long each choghadiya slot lasts — depends on knowing the exact moment of sunrise for a given location. A difference of even a few minutes in the sunrise time can shift slot boundaries and, in edge cases, change which tithi is considered the ruling tithi of the day.

Sunrise and sunset in panchang contexts refer to the moment the upper limb of the Sun's disc appears at (or disappears below) the true horizon, corrected for atmospheric refraction. Standard refraction at the horizon is approximately 34 arcminutes, and the Sun's semi-diameter adds another 16 arcminutes, meaning the geometric center of the Sun is about 50 arcminutes below the horizon at the moment of visible sunrise. Altitude, temperature, and pressure can further affect refraction, though standard conditions are assumed for panchang computation.

Tithimala computes sunrise and sunset using Swiss Ephemeris, which models the Sun's apparent position with high precision, accounting for the equation of time, the observer's geographic latitude and longitude, and standard atmospheric refraction. For any city or GPS coordinate the user provides, the engine produces sunrise and sunset times accurate to within seconds. This is critical because the daylight duration derived from these times is the foundation for computing Rahu Kaal (8 equal divisions), choghadiya (8 equal daytime + 8 nighttime slots), and hora (planetary hour) timings.

The emphasis on sunrise precision reflects a deeper principle in Vedic timekeeping: natural astronomical events, not arbitrary clock conventions, define the rhythm of sacred time. This is why panchangs have always been location-specific — a panchang computed for Varanasi cannot be used in Bangalore without recalculation.